Liquid crystal display for projection systems

ABSTRACT

Disclosed is a liquid crystal display unit comprising liquid twisted nematic liquid crystal material sandwiched between two polarizers. Transparent electrodes are provided on each side of the layer of liquid crystal for locally energizing liquid crystal material in the vicinity of two energized transparent electrodes. Polarized light passing through one polarizer is twisted or not twisted depending upon the energization state of the liquid crystal material and depending upon the second polarizer orientation does or does not pass therethrough. Accordingly, depending upon energization locations, images are formed which can be projected upon a screen. In preferred embodiments the liquid crystal display unit is used in conjunction with a cabinet to provide a low stress work station. A further embodiment includes a folded optical path in combination with the liquid crystal display so as to provide a compact projector. When operating in conjunction with an overhead projector, a preferred embodiment of the present invention is powered by light energy from the overhead projector and in a further preferred embodiment is controlled through the use of infrared or other non-visible electromagnetic communication.

RELATED APPLICATIONS

This application is a continuation of U.S application Ser. No.07/625,037 filed Dec. 10, 1990 which is a continuation-in-part of U.S.Ser. No. 07/194,516 filed May 16, 1988 which issued as U.S. Pat. No.4,976,536 on Dec. 11, 1990, which in turn is a divisional of U.S. Ser.No. 07/044,332 filed Apr. 30, 1987 now U.S. Pat. No. 4,763,993 issuedAug. 16, 1988.

BACKGROUND AND SUMMARY OF THE INVENTION

1. Field of the Invention

The present invention relates to projection systems in general, andspecifically to a liquid crystal display system for use in conjunctionwith an overhead projector for displaying computer generated images.

2. Discussion of the Prior Art

The use of a liquid crystal display (LCD) in conjunction with aconventional overhead projector is disclosed in U.S. Pat. No. 4,154,007issued to Wallace P. Judd. The Judd patent describes an electroniccalculator modified so as to permit light to pass through the top andbottom plates of an LCD. This allows the calculator to be placed onto aconventional overhead projector thereby projecting an enlarged image ofthe calculator LCD on the projection surface. The LCD in Judd appears tobe comprised of smectic crystals which, when not energized by anelectric field, are transparent to light passing therethrough but becomeopaque to this light when energized. The opacity is due to the fact thatenergizing of the crystals places them in a disorganized state whichcauses light to be scattered in all directions. Because the smecticcrystals only change the character of light passing through (fromunscattered to scattered) much of the light and heat energy passesthrough the crystals. Unfortunately because the light is only alteredslightly smectic displays tend to have a relatively low contrast.

Additionally to avoid excess drive circuitry and electricalinterconnections, most LCD displays are multiplexed which means thateach portion of the display is addressed (or energized) for only afraction of the time. In a twelve digit calculator display, each digitwould be addressed only one-twelfth of the time or it can be said thatthe display has a 1/12 duty cycle.

In order to improve contrast, modern calculators have changed to twistednematic crystal displays which, if multiplexed at relatively high dutycycles, such as those associated with simple calculators, can producehigh contrast readability. Such displays require the use of polarizers.Although polarizers tend to cause the display to absorb more heat andthus reduce the contrast, the high initial contrast obtainable with thehigh duty cycle calculator display could tolerate the heat withoutcontrast being objectionably reduced. If the Judd-type patent weremodified to utilize such a twisted nematic crystal display, the heatassociated with an overhead projector would probably not cause anyserious difficulty in its operation because of the high duty cycle.

However, where a higher resolution display is desired, for example a 25line by 80 column and/or graphic display, a much lower duty cycle isavailable with respect to energization of each element, i.e., on theorder of 1/100. Smectic crystals are unworkable because of theirinherent low contrast. The very low duty cycle also makes the contrastavailable from twisted nematic crystal displays marginal and, whencombined with the contrast reduction caused by polarizer heating, suchdisplays are impractical.

A typical projector has a high power incandescent or halogen lamputilizing 250 to 500 watts or more during operation. In many instances90% of the radiation generated by the lamp is in the infrared or heatproducing frequency range. Excess temperatures can be harmful to liquidcrystal displays causing their destruction if high enough. However, evenbelow the destructive temperature level, the effect of high temperaturesis to decrease LCD contrast.

The optics of most conventional projectors also tends to exacerbate theheat problem. The projectors in general focus the light beam so that itimpinges upon a lens (generally of the Fresnel type) upon which theprojected material (in this case the LCD) is placed. The function ofthis lens is to direct the light so that it passes through theprojection optics thus achieving the brightest possible projected image.While the attempt is made to focus light on the lens as uniformly aspossible, the light energy may vary by as much as 50% or more from a"hot spot" in the center of the lens to the edges. Because it isnecessary to have enough light so that the edges of the display arereadily visible, this means that the temperature effects due to the hotspot in the center are even greater than elsewhere on the display.

Although some rather expensive overhead projectors tend to reduce theheat problem by arrangements of heat-absorbing and/or heat-reflectingglass or filters, the lower cost projectors make little attempt toreduce heat at the display surface. It is desirable that any LCDprojection system be able to utilize any projecting apparatus.

A further problem in the use of LCD systems with overhead projectors isthe requirement for an external power supply and a data input cordrendering such systems cumbersome to use.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a liquidcrystal display apparatus compatible for use with all overheadprojectors providing high contrast readability.

It is a further object of the present invention to provide an LCDdisplay for use with an overhead projector which has no external powercord connection.

It is a further object of the present invention to provide an LCDdisplay for use with an overhead projector where the display requires noexternal power or data input connecting cord.

It is a still further object of the present invention to provide anintegrated projection system for projecting computer or graphic displayinformation.

It is an additional object of the present invention to provide anintegrated low visual stress work station for displaying high resolutioninformation.

It is a still further object of the present invention to provide adesktop projector of high resolution information where the projector isextremely compact and portable.

The above and other objects are achieved in accordance with the presentinvention by utilizing a light transparent insulation means and apolarizer or back polarizing filter between the light source and thetwisted nematic crystal display. The analyzer or front polarizing filteris located between the twisted nematic crystal display and theprojection screen. The use of transparent conductors on the LCDfacilitates localized energization of the twisted nematic crystal whereit is desirable to produce a change in opacity of the display.

In one embodiment, a heat reflective film is the light transparentinsulation means and is utilized to further reduce the heat input to thetwisted nematic crystal. In a further embodiment, the liquid crystaldisplay is powered by solar cells located on the display for convertinga portion of the overhead projector light energy to electrical energyfor use in the display eliminating the need for a separate power cable.In a still further preferred embodiment, the computer or other controlmeans communicates with the display through a wireless communicationsystem eliminating the need for any external cables connected to thedisplay. In a further embodiment, the display is combined with aprojector resulting in a compact low cost projection system. In afurther preferred embodiment the display is utilized in conjunction witha lower power projector in a computer or word processing work station toprovide a low visual stress display system. In an additional embodiment,the combination of folded optics, a "cold mirror" and the LCD provide acompact and portable desktop electronic information projector.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof will be readily apparent by reference to theaccompanying drawings, wherein:

FIG. 1 is a schematic representation of the effect of a twisted nematiccrystal display;

FIG. 2 is a side exploded view of a twisted nematic crystal display inaccordance with the present invention;

FIGS. 3a and 3b are side exploded views of twisted nematic crystaldisplays in accordance with a further embodiment of the presentinvention;

FIG. 4a shows the present invention being utilized with a conventionaloverhead projector;

FIG. 4b illustrates an integrated overhead projector combined with anLCD display in accordance with the present invention;

FIGS. 5a and 5b illustrate low stress work stations in accordance withthe present invention with conventional light source and a point lightsource, respectively;

FIGS. 6a and 6b illustrate an elastomeric connector and its use inassembly of one embodiment of the present invention, respectively;

FIGS. 7a and 7b show a flex circuit connector and its use in theassembly of one embodiment of the present invention, respectively; and

FIG. 8 is a side view partially in section of a further embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates the operation of a liquid crystal material situatedbetween two polarizers. A light source 10 will emit light having nospecific polarization. However, light passing through polarizer or backpolarizing filter 12 will have only a vertical orientation as it enterstwisted nematic liquid crystal material 14. In the illustratedembodiment, in unenergized area 16, the local region where the liquidcrystal is unenergized, the light polarization is rotated a specificangle (such as the 90°shown) which changes it to a horizontalpolarization which passes through analyzer or front polarizing filter18. However the energized area 20 of the liquid crystal display allowslight to pass through without its polarity being twisted and thevertically polarized light would be blocked by the horizontallypolarized analyzing filter 18. Thus in FIG. 1 as shown energized areasof the liquid crystal would be dark and unenergized areas would belight. Thus one would have dark graphics on a light background. Ifeither polarizers were rotated approximately 90° the effect would bereversed, allowing light to be transmitted where the liquid crystal isenergized and for light to be blocked where the liquid crystal is notenergized, providing a light graphics on a dark background.

FIG. 2 illustrates the basic embodiment of applicant's invention. Thetwisted nematic liquid crystal material 14 is bounded by sealingmaterial 22 and contained between two transparent plates 24. Amultiplicity of transparent electrodes 26 extending across the figureare orthogonal to a multiplicity of transparent electrodes 28 whichextend generally in a direction perpendicular to the plane of thedrawing. When pairs of these electrodes are simultaneously addressed,they serve to energize the twisted nematic liquid crystal material 14 inthe immediate vicinity of the junction of the energized electrodes. Thecriss-crossing multiplicity of electrodes comprises a means for locallyenergizing the crystal material in response to the control unit 30through a multiplicity of control wires 32 and 34. Power to operatecontrol unit 30 can be supplied externally or, in an embodiment shown inFIG. 2, through solar cell 36 which converts a portion of theillumination from the projector itself into electricity.

Information to the control unit 30 on which electrodes are to beenergized or de-energized can be provided through an external connectingcable to the computer providing image information or in the preferredembodiment shown in FIG. 2 through an infrared control receiver 38 whichis responsive to infrared transmissions from a transmitting devicesimilar to infrared television and video cassette recorder transmitters.In the preferred embodiment shown in FIG. 2 no external connections atall will be necessary to power or control the device rendering itextremely easy to use. In FIG. 2 polarizer 12 could include an infraredmirror which allows visual light to pass but serves to reflect theinfrared (heat-producing) portion of the light 11 from the light source.

In a preferred embodiment, the liquid crystal display panel in FIG. 2would utilize a heat reflecting film 47 adjacent or separated frompolarizer 12 to reduce the amount of heat passing through the liquidcrystal material 14. A preferred embodiment utilizes a heat reflectingfilm 47 marketed under the trademark Altair-M by Southwall Technologiesin Palo Alto, Calif. The Altair-M coating is sputter-deposited andresults in a film that has visible light transmissivity and alsoelectrical conductivity. Electrical conductivity is advantageous in thatit helps prevent broadcast of electromagnetic interference beyond theconfines of the display device. The film additionally has superiorenvironmental stability over many other coating processes althoughadditional sheets of glass can be used to protect the film and/orpolarizer from scratching.

Alternate embodiments of the transparent portion of the display unit areshown in exploded views of FIGS. 3a and 3b. In addition to the otherpreviously discussed components, FIG. 3a illustrates a further plate 40which, with polarizer 12, is separated from transparent plate 24 byspacing material 42. In a preferred embodiment, the spacing materialcould be permeable to air and water vapor but impermeable tocontaminants such as dust, thereby reducing any degradation over a time.In the FIG. 3a embodiment a single insulating or air space 44 serves tofurther insulate the temperature sensitive twisted nematic liquidcrystal material 14 from heat transmitted from the light source 10.

In extreme temperature and humidity environments, it may be desirable toutilize the variation shown in FIG. 3b which includes two plates 40 andtwo sets of impermeable spacers 43 forming two air spaces 44 forproviding greater insulation. The spacers 43 are shown with inlets 46and outlets 48. The inlets 46 are connected to a coolant supply 49 whichmay be any transparent fluid. The fluid, in a preferred embodiment air,flows through the spaces on one or both sides of the liquid crystalmaterial 14 cooling it during operation. The before mentioned heatreflecting film 47 is also illustrated. Of course the embodiments ofFIG. 3a and 3b could also utilize the previously discussed infraredmirrors as back plates 40 in order to reflect any infrared light awayfrom the liquid crystal material 14.

FIG. 4a illustrates the use of the display unit 8 in combination with aconventional overhead projector 50. Projector 50 includes a lowerportion 52 housing the light source and initial reflecting and focusingmirrors and lenses, and an upper mirror/lens assembly 54. Display unit 8is placed over the normal projection surface and includes an aperture 56which corresponds to the visible light transparent portion of thedisplay unit. Solar cells 36, not shown because they are on the lowerportion of the display unit 8, could provide sufficient electrical powerto run the control unit and the energization and de-energization of thevarious transparent electrodes in the unit. Information concerning whichelectrodes are to be energized and de-energized can be supplied by meansof infrared receiver 38. Thus it can be seen that display unit 8 isquite portable and can be used with any existing overhead projectorsystem and the use of the solar cell and infrared data link eliminateany problem with cords.

In FIG. 4b a further preferred embodiment is illustrated in which thedisplay unit portion 8 is built in to the overhead projector 60. Becausethis unit is not as portable it may not be quite as convenient althoughthe fact that the display unit is part of the lower portion 52eliminates the need for solar cell installation on the unit in order topower the control unit and a simple internal conductor connection willsuffice. Similarly, there is no need to utilize infrared receiver 38 asa direct computer connection to the display unit 8 through lower portion52 can easily be accomplished. However, it may be desirable to retainthe infrared receiver 38 so that the projected image can be ultimatelycontrolled from a remote location.

The present invention can also be utilized in conjunction with or builtinto a low stress work station for computer/word processing operators orany other individuals who would normally work in front of a monitor or acathode ray tube (CRT) screen. Normal viewing distances from an operatorto a keyboard is about 24 inches and from the operator to the CRT isabout 28 to 30 inches. It has been found that if a display can beprovided at a further distance from the operator but with largercharacters (so that the viewing angle subtended by the character isequal to or greater than that of the CRT) much less visual stress iscreated.

Contrast ratio is concerned with differences in the brightness betweenthe viewed information and the immediate background and between theimmediate background and the larger surround. A difference between lightinformation on a dark CRT display and black information on a whiteprinted page is that the informational elements in the display areluminous and are seen by direct rather than reflected light. Contrastratios for the CRT display for comfortable viewing can be rather lowwith values of 2 or even less. Because the informational content of atypical CRT display is less than about 5% of the display area, thesparseness of luminosity causes the eye to adapt to the generally darkbackground. However, many times the luminance of the presentedinformation is increased in an attempt to overcome the effects ofreflections, glare, etc. and it is this increased luminosity which leadsto increased viewing stress. An operator at a display seldom spends morethan 25% of their time viewing the display and the remainder of theirtime is spent looking around at the keyboard, reference materials, atdistractions or simply for a rest. Because all of these areas differ inluminance, the eye must continually change aperture to adapt to thedifferences in luminance. Stress because of this continuous adaptationcan be minimized if the contrast ratios between these various areas areall kept to relatively low values. CRT displays are generally relativelysmall and thus occupy only a small portion of the visual field. A largerdisplay occupying a greater portion of the visual field together withproper lighting control in the surrounding areas leads to lowered stresslevels.

Reflection and glare are also problems, are important sources of stressand in many instances are outside of the control of the operator.Because a conventional CRT display has a convex surface, it providesreflections over a wide field of view. The inability to reposition a CRTdisplay so as to eliminate all substantial reflections can causeadditional visual stress. Focus and flicker are additional problemscausing visual stress. A cathode ray tube display is electronicallyfocused and over a period of time the focus may drift causing thedisplay to go slightly out of focus. Additionally because of the CRTline scan, frame rates on the order of 50 to 60 Hertz are generated.Some flicker perception is obtained even at these high frame ratesleading to additional visual stress.

In order to overcome a number of problems relating to visual stress inthe workplace, applicant's invention can be utilized in conjunction withor incorporated into a low stress work station, examples of which areshown in FIGS. 5a and 5b. Both arrangements in FIGS. 5a and 5b wouldprovide for an image width of around 36 inches allowing for viewing at adistance of at least 36 inches. FIG. 5a utilizes an enclosure with theconventional light source 10 providing illumination through a Fresnellens 70 to the display unit 8 whereupon the light passes throughprojection lens 72, is reflected by front surface mirror 74 onto rearprojection screen 76.

The embodiment in FIG. 5b does not require any refractive opticalelements such as Fresnel lens 70 or projection lens 72 and insteadutilizes an extremely small point light source 78 and the directtransmission of the light through display unit 8 reflecting off of frontsurface mirror 74 onto the rear projection screen 76. This embodimenthas a significantly shorter optical path than that of FIG. 5a andoperates similarly to the well known shadowgraph technique. Obviouslybecause of their different locations in the view screens, the displayunit in FIG. 5a would provide the reverse image on the rear projectionscreen 76 as opposed to the image provided by the display unit in FIG.5b. This reversal as between the two different work stations can beaccommodated mechanically by turning over the display unit 8 (assumingthat the temperature and insulating qualities and components of thedisplay unit are not critical to its operation or that it has the sameinsulating capabilities on both sides of the liquid crystal display) orby merely correcting for this in the electronic control unit or theoperating software.

The advantages of the low stress work station displays are that thehigher brightness level of the display background (much closer to thenormal surround luminosity) and the lower contrast ratio between theimage and the display background tends to reduce the stress due toscreen and image brightness. The greater viewing distance especially ata distance where the eye tends to operate with a greater depth of focustends to reduce stress due to changes in focus required with headmovement. Larger image sizes and the larger visual angle subtended tendsto improve readability and allow for a less precise focus. Also, with akeyboard and a normal CRT they are roughly the same distance from theeye, causing the eye to maintain the same focus all the time. Becausethe work station display is substantially farther from the eye than thekeyboard, the eyes focus must change in shifting back and forth, thusproviding a "restful exercise." The large screen size relative to thefield of view tends to reduce stress due to differences in brightnessbetween the display screen and the visual surround. The liquid crystaldisplay unit being digital in nature (energized area or pixel only atcross points between transparent conductors) tends to reduce stress dueto display focus or lack thereof. Low contrast ratio of the display unittends to reduce stress due to flicker. The flat rear projection screen76 tends to reduce stress from reflections and reduce reflected glare.Often times the flat screen can be repositioned to avoid undesirablereflections altogether.

Various preferred embodiments for packaging a display unit 8 have beenexamined and found suitable. Although FIG. 2 illustrates an explodedview of the device with only one edge housing the control unit beingshown, in practice each unit would have an inner transparent imagegenerating area surrounded by an outer frame or other structure. FIG. 2illustrates the use of control wires 32 and 34 to connect the energizingelectrodes 26 and 28 to the control unit 30, but one preferredembodiment applicant's invention utilizes an elastomeric connector 80and a portion of such a connector is shown in FIG. 6a.

The elastomeric connector 80 includes a pair of insulating strips 81sandwiching conductive elements 82 and non-conductive elements 83 in analternating fashion. The application of such an elastomeric connector isillustrated in FIG. 6b which includes an LCD panel 86 which is thetransparent portion of the display unit shown in FIG. 2 or the unitsshown in FIGS. 3a and 3b. A display driver board 88 is comprised ofprinted circuit boards and/or elements making up the electronic controlunit 30, solar cell 36 and/or infrared receiver 38. The elastomericconnectors serve to provide conduction paths between the driver boardand the transparent electrodes located in the LCD panel. Appropriateconnector pads would be located on the LCD panel and similar pads wouldbe provided on the driver board 88. Edge clamps 90 (represented byarrows in FIG. 6b) would serve to firmly compress the elastomericconnector between the pads on the LCD panel 86 and on the driver board88. Although it cannot be seen in this view, the driver board 88 wouldobviously have a substantial aperture in the board so that light couldpass therethrough and consequently through the LCD panel for imagedisplay purposes.

A further alternative connection method is that of flex circuit 92 shownin FIG. 7a. The flex circuit utilizes a flexible insulative substrate 94upon which electrical conductors 96 have been painted or otherwisedeposited. The use of such a flex circuit is shown in FIG. 7b in whichthe conductive portions of the flex circuit are connected to theappropriate portions of driver board 88 on the one hand and theappropriate transparent electrodes in the LCD panel on the other hand.In this manner the display unit can be folded easily and inexpensivelyduring manufacture. The final position of both driver boards is shown inphantom lines in FIG. 7b and the initial manufacturing position of therighthand driver board is also shown in phantom lines.

A further embodiment of the present invention is a portable and compactdesktop information projector 100 shown in FIG. 8. Instead of supplyinginformation to essentially one operator as in the low stress workstation, it is envisioned that there is a need for a projection systemcapable of being viewed by 3 to 5 people simultaneously for theprojection of electronic data information. It is desirable that such asystem be completely self-contained although it is envisioned thatsubstantially lower projection lamp intensities will be required due tothe much smaller projection area as compared to that of the conventionaloverhead projector.

In FIG. 8, the low power light source 102 provides an initial beam oflight toward first mirror 104 which may advantageously be a "coldmirror", i.e., one which reflects visible light but passes infraredlight. If mirror 104 is a "cold mirror" much of the heat from lightsource 102 would be passed to the righthand portion of the enclosure andcould then be radiated to the room. The beam of light reflected bymirror 104 passes through Fresnel lens 105 and the LCD display 106 whichmay be similar to those described with reference to FIGS. 2, 3a or 3b.Light is then reflected from second mirror 108 and third mirror 110through lens system 112 to a fourth mirror 114 and from there onto theprojection surface 116. Electronic data information may be entered intothe projector by means of a computer and/or keyboard 118 which isconnected (not shown) to control unit 30 which is also connected (notshown) to the LCD display 106. The focus of lens system 112 can becontrolled by adjuster 120.

In order to obtain suitable image clarity at the projection surface 116it is desirable to have the largest LCD display 106 available. However,in order to avoid the necessity for extremely complex, and thusexpensive, lens systems, it is necessary to have the longest opticalpath possible. In FIG. 8 the optical path is folded four times allowingfor the components to be arranged in a relatively compact fashion andstill provide a high resolution projection with a relatively inexpensivelens system. If a "cold mirror" is used for the first mirror 104 it maybe unnecessary to provide any further heat insulation or temperatureprotection for the LCD display 106 in view of the relatively low powerlight source 102.

The desktop information projector 100 is quite portable and yet willprovide a high contrast image suitable for viewing by a plurality ofoperators and may be extremely useful for teaching and demonstratingcomputers, computer-generated graphic systems, etc. mirror" which passesinfrared but reflects visible light.

In accordance with the above, it will be seen that applicant's liquidcrystal display unit can be utilized with any conventional overheadprojector to provide computer generated images in a projection format.It will be seen that the basic display unit will have a relatively lowcost and due to solid state technology will be extremely reliable. Thedevice is capable of providing image animation and the image content isalterable in real time by means of the computer control connection. Thedevice is also extremely portable and is compatible with all overheadprojection systems. In combination with an appropriate work stationhousing the display unit can provide an extremely low stress work placewhen replacing the more conventional CRT.

The desktop information projector and the low stress work station canalso be used in many situations in which the presence of a rear or frontprojector, respectively, would be undesirable. Examples would be pointof sale or store window displays, restaurant and cafeteria displays,transportation terminal displays of arrival and departure times, outdoordisplays in which only the screen need be outdoors and the moreexpensive contents are protected from the weather, vandalism, etc.,large letter paging systems that can change or retain informationwithout dependence upon clear or repeated voice communication.

In view of the above disclosure, many modifications and applications ofthe present invention will be obvious to those of ordinary skill in theart. Therefore, the present invention is limited only by the claimsappended hereto.

What is claimed is:
 1. A compact information projector for projectingelectronically generated display images on a remote surface, said imagesbased upon electronic signals, said projector comprising:a light sourcefor projecting a beam of light along an optical path; twisted nematicliquid crystal display, located in said optical path, for controllingpolarization of light passing therethrough in response to localizedenergization and de-energization of said liquid crystal display inaccordance with said electronic signals; at least a first reflectingmirror located in said optical path and directly optically between saidlight source and said liquid crystal display, where directly opticallybetween is defined as both visible and infrared light from said lightsource being reflected only by said reflecting mirror before itencounters said liquid crystal display; at least one infrared reflector,located in said optical path and optically between said light source andsaid twisted nematic liquid crystal display, said at least one infraredreflector reflects infrared light and passes visible light; at least oneFresnel lens, located in said optical path between said light source andsaid twisted nematic liquid crystal display, for collimating lightpassing through said liquid crystal display; a light transparent airspace, said air space having an air entrance and an air exit, said airspace located on said optical axis and between said liquid crystaldisplay and said light source; a fan, associated with one of said airentrance and said air exit, for moving air through said lighttransparent air space and for cooling said liquid crystal display; atleast a second reflecting mirror, located in said optical path betweensaid liquid crystal display and said remote surface; a control,responsive to said electronic signals, for selectively and locallyenergizing said liquid crystal display; a back polarizer, disposed insaid beam and located between said crystal means and said light source,for polarizing light passing therethrough; and a front analyzer,disposed in said beam and located between said liquid crystal displayand said remote surface, for allowing light of a selected polarizationto pass therethrough and for blocking light not having said selectedpolarization.
 2. A compact information projector for projectingelectronically generated display images on a remote surface, said imagesbased upon electronic signals, said projector comprising:means forprojecting a beam of light along an optical path, said projecting meansincluding a light source; twisted nematic crystal means, located in saidoptical path, for controlling polarization of light passing therethroughin response to localized energization and de-energization of saidcrystal means in accordance with said electronic signals; at least onemirror means, located optically between said light source and saidtwisted nematic crystal means, said at least one mirror means comprisesmeans for reflecting visible light and for passing infrared light; atleast one infrared reflector means located optically between said lightsource and said twisted nematic crystal means, said at least oneinfrared reflector means comprises means for reflecting infrared lightand for passing visible light; means, responsive to said electronicsignals, for selectively and locally energizing said crystal means,;back polarizing means, disposed in said beam and located between saidcrystal means and said light source, for polarizing light passingtherethrough; and front analyzing means, disposed in said beam andlocated between said crystal means and said remote surface, for allowinglight of a selected polarization to pass therethrough and for blockinglight not having said selected polarization.
 3. The projector accordingto claim 2, further including a plurality of mirrors located in saidoptical path.
 4. The projector according to claim 3, wherein there isfurther included lens system means, located in said optical path, forfocusing said electronically generated display images on said remotesurface.
 5. The projector according to claim 4, wherein said lens systemmeans includes a means for adjustably focusing said display images onsaid remote surface.
 6. The projector according to claim 2, wherein saidat least one mirror means is located optically between said infraredreflector means and said light source.
 7. The projector according toclaim 2, wherein said at least one mirror means comprises a firstreflecting mirror, said first reflecting mirror is in a plane and hasentrance and exit angles, and said plane makes an angle of substantially45° with said optical path with respect to both the entrance and exitangles.
 8. The projector according to claim 2, wherein, there is furtherincluded a second reflecting mirror, located in said optical pathbetween said crystal means and said remote surface, said secondreflecting mirror is in a plane and has entrance and exit angles, andsaid plane makes an angle of substantially 45° with said optical pathwith respect to both the entrance and exit angles.
 9. The projectoraccording to claim 2, wherein said at least one mirror means comprises afirst reflecting mirror and further including a second reflectingmirror, located in said optical path between said crystal means and saidremote surface, said first and second reflecting mirrors are inrespective planes and each of said first and second reflecting mirrorshave entrance and exit angles, and said respective planes make angles ofsubstantially 45° with said optical path with respect to both theentrance and exit angles and the planes are at right angles with respectto one another.
 10. The projector according to claim 2, wherein saidinfrared reflector means is located between said at least one mirrormeans and said crystal means.
 11. The projector according to claim 2,wherein said infrared reflector means is comprised of an infraredreflecting film.
 12. The projector according to claim 2, furtherincluding at least one Fresnel lens, located in said optical pathbetween said light source and said twisted nematic crystal means, forcollimating light passing through said crystal means, wherein said atleast one Fresnel lens is located between said first reflecting mirrorand said infrared reflecting means.
 13. The projector according to claim2, further including means for defining a light transparent air space,said air space having an air entrance and an air exit, said air spacelocated on said optical axis and between said crystal means and saidlight source, wherein said means for defining a light transparent airspace comprises a means for spacing said infrared reflector means fromsaid crystal means.
 14. The projector according to claim 13, furtherincluding means, associated with one of said air entrance and said airexit, for moving air through said light transparent air space and forcooling said crystal means, wherein said means for moving is associatedwith said air entrance and comprises a coolant supply means forproviding air to said air entrance.
 15. The projector according to claim2, wherein said selectively and locally energizing means comprises afirst plurality of conductors and a second plurality of conductors atleast partially crossing said first plurality of conductors, such thatwhen a single conductor from said first plurality and a single conductorfrom said second plurality are energized, said crystal means isenergized in the vicinity of the crossing of said single conductors. 16.A compact information projector for projecting electronically generateddisplay images on a remote surface, said images based upon electronicsignals, said projector comprising:means for projecting a beam of lightalong an optical path, said projecting means including a light source;twisted nematic crystal means, located in said optical path, forcontrolling polarization of light passing therethrough in response tolocalized energization and de-energization of said crystal means inaccordance with said electronic signals; at least one mirror means,located directly optically between said light source and said twistednematic crystal means, said at least one mirror means comprises meansfor reflecting visible light and for passing infrared light, wheredirectly optically between is defined as visible light from said lightsource being reflected only by said at least one mirror means before itencounters said twisted nematic crystal means; means, responsive to saidelectronic signals, for selectively and locally energizing said crystalmeans,; back polarizing means, disposed in said beam and located betweensaid crystal means and said light source, for polarizing light passingtherethrough; and front analyzing means, disposed in said beam andlocated between said crystal means and said remote surface, for allowinglight of a selected polarization to pass therethrough and for blockinglight not having said selected polarization.
 17. The projector accordingto claim 16, further including a plurality of mirrors located in saidoptical path.
 18. The projector according to claim 16, wherein there isfurther included lens system means, located in said optical path, forfocusing said electronically generated display images on said remotesurface.
 19. The projector according to claim 18, wherein said lenssystem means includes a means for adjustably focusing said displayimages on said remote surface.
 20. The projector according to claim 16,wherein said at least one mirror means is in a plane and has entranceand exit angles, and said plane makes an angle of substantially 45° withsaid optical path with respect to both the entrance and exit angles. 21.The projector according to claim 16, wherein, there is further includeda reflecting mirror, located in said optical path between said crystalmeans and said remote surface, said reflecting mirror is in a plane andhas entrance and exit angles, and said plane makes an angle ofsubstantially 45° with said optical path with respect to both theentrance and exit angles.
 22. The projector according to claim 16,further including a reflecting mirror, located in said optical pathbetween said crystal means and said remote surface, said mirror meansand reflecting mirror are in respective planes and have entrance andexit angles, said respective planes make angles of substantially 45°with said optical path with respect to both the entrance and exit anglesand the planes are at right angles with respect to one another.
 23. Theprojector according to claim 16, further including at least one infraredreflector means for reflecting infrared light and for passing visiblelight, said infrared reflector means is located between said at leastone mirror means and said crystal means.
 24. The projector according toclaim 23, wherein said infrared reflector means is comprised of aninfrared reflecting film.
 25. The projector according to claim 16,further including at least one Fresnel lens, located in said opticalpath between said light source and said twisted nematic crystal means,for collimating light passing through said crystal means, wherein saidat least one Fresnel lens is located between said mirror means and saidcrystal means.
 26. The projector according to claim 16, furtherincluding means for defining a light transparent air space, said airspace having an air entrance and an air exit, said air space located onsaid optical axis and between said crystal means and said light source,wherein said means for defining a light transparent air space comprisesa means for spacing said back polarizer means from said crystal means.27. The projector according to claim 26, further including means,associated with one of said air entrance and said air exit, for movingair through said light transparent air space and for cooling saidcrystal means, wherein said means for moving is associated with said airentrance and comprises a coolant supply means for providing air to saidair entrance.
 28. The projector according to claim 16, wherein saidselectively and locally energizing means comprises a first plurality ofconductors and a second plurality of conductors at least partiallycrossing said first plurality of conductors, such that when a singleconductor from said first plurality and a single conductor from saidsecond plurality are energized, said crystal means is energized in thevicinity of the crossing of said single conductors.
 29. A compactinformation projector for projecting electronically generated displayimages on a remote surface, said images based upon electronic signals,said projector comprising:means for projecting a beam of light along anoptical path, said projecting means including a light source; twistednematic crystal means, located in said optical path, for controllingpolarization of light passing therethrough in response to localizedenergization and de-energization of said crystal means in accordancewith said electronic signals; at least a first reflecting mirror locatedin said optical path and directly optically between said light sourceand said twisted nematic crystal means, where directly optically betweenis defined as both visible and infrared light from said light sourcebeing reflected only by said reflecting mirror before it encounters saidtwisted nematic crystal means; at least one infrared reflector meanslocated in said optical path and optically between said light source andsaid twisted nematic crystal means, said at least one infrared reflectormeans comprises means for reflecting infrared light and for passingvisible light; at least one Fresnel lens, located in said optical pathbetween said light source and said twisted nematic crystal means, forcollimating light passing through said crystal means; means for defininga light transparent air space, said air space having an air entrance andan air exit, said air space located on said optical axis and betweensaid crystal means and said light source; means, associated with one ofsaid air entrance and said air exit, for moving air through said lighttransparent air space and for cooling said crystal means; at least asecond reflecting mirror, located in said optical path between saidtwisted nematic crystal means and said remote surface; means, responsiveto said electronic signals, for selectively and locally energizing saidcrystal means; back polarizing means, disposed in said beam and locatedbetween said crystal means and said light source, for polarizing lightpassing therethrough; and front analyzing means, disposed in said beamand located between said crystal means and said remote surface, forallowing light of a selected polarization to pass therethrough and forblocking light not having said selected polarization.
 30. The projectoraccording to claim 29, further including a plurality of mirrors locatedin said optical path.
 31. The projector according to claim 29, whereinthere is further included lens system means, located in said opticalpath, for focusing said electronically generated display images on saidremote surface.
 32. The projector according to claim 31, wherein saidlens system means includes a means for adjustably focusing said displayimages on said remote surface.
 33. The projector according to claim 29,wherein said first reflecting mirror is in ak plane and has entrance andexit angles, and said plane makes an angle of substantially 45° withsaid optical path with respect to both the entrance and exit angles. 34.The projector according to claim 29, wherein said second reflectingmirror is in a plane and has entrance and exit angles, and said planemakes an angle of substantially 45° with said optical path with respectto both the entrance and exit angles.
 35. The projector according toclaim 29, wherein said first and second reflecting mirrors are inrespective planes and each of said first and second reflecting mirrorshave entrance and exit angles, and said respective planes make angles ofsubstantially 45° with said optical path with respect to both theentrance and exit angels and the planes are at right angles with respectto one another.
 36. The projector according to claim 29, wherein saidinfrared reflector is located between said first reflecting mirror andsaid crystal means.
 37. The projector according to claim 29, whereinsaid infrared reflector means is comprised of an infrared reflectingfilm.
 38. The projector according to claim 29, wherein said at least oneFresnel lens is located between said first reflecting mirror and saidinfrared reflecting means.
 39. The projector according to claim 29,wherein said means for defining a light transparent air space comprisesa means for spacing said infrared reflector means from said crystalmeans.
 40. The projector according to claim 29, wherein said means formoving is associated with said air entrance and comprises a coolantsupply means for providing air to said air entrance.
 41. The projectoraccording to claim 29, wherein said selectively and locally energizingmeans comprise a first plurality of conductors and a second plurality ofconductors at least partially crossing said first plurality ofconductors, such that when a single conductor from said first pluralityand a single conductor from said second plurality are energized, saidcrystal means is energized in the vicinity of the crossing of saidsingle conductors.